In the absence of this feedback, chordotonal mutant flies are somewhat ataxic ( Eberl et al., 2000). In the adult, the femoral chordotonal organs (fCHO) comprise three clusters totaling about 74 scolopidia ( Figure 2) per leg ( Shanbhag et al., 1992) and provide proprioceptive feedback. In the larva, the eight scolopidia (five of them shown in Figure 1) per abdominal hemisegment provide touch sensitivity and during locomotion they provide sensory feedback to the locomotor circuit ( Kernan et al., 1994, Caldwell et al., 2003). The diverse chordotonal organs of Drosophila almost certainly derive from a common ancestral mechanosensor whose developmental genetic program has been modified in multiple ways to generate chordotonal organs of distinct sizes and functions. Selection pressures on the functions of specific sense organs have long-term effects on whether those functions will be maintained and further perfected, whether functions will be attenuated, even lost, or whether novel functions will arise. Second, we highlight some important questions raised by these considerations, the answers to which will represent significant advances in the decade(s) to come.ĭrosophila chordotonal organs and their functions Instead, the Drosophila JO represents an evolution to a highly specialized organ for hearing, clearly chordotonal in nature, but with some features as different from ancestral proprioceptors as the butterfly is from the caterpillar. In this paper, we first focus on advances that reinforce the emerging conclusion that the JO is much more than a mere recapitulation of the canonical larval chordotonal sense organ type. Several reviews have summarized aspects of this progress ( Eberl, 1999, Caldwell and Eberl, 2002, Jarman, 2002, Robert and Göpfert, 2002, Todi et al., 2004, Boekhoff-Falk, 2005). Thus, Drosophila hearing research has metamorphosed into an exciting research field that ties together intricate physiological and mechanical mechanisms with complex developmental biology. These include mutagenesis screens, gene expression patterns and other candidate gene approaches including homology to known human hereditary hearing loss genes-almost all of which have been identified over the same time period. The Johnston’s organ (JO), located in the fly’s antenna, formally has been confirmed as the major auditory organ and mutations in many genes required for hearing have been identified using a variety of approaches. Practically the entire progress in genetic and molecular elucidation of hearing mechanisms in the fruitfly, Drosophila melanogaster has occurred in the last decade.
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